Abstract More than 10 million U.S. adults, including 165,000 veterans who use Veterans Affairs (VA) medical facilities, have class III obesity [body mass index (BMI)e40 kg/m 2]. The impact of this epidemic is substantial; in 2000, class III obesity was associated with 82,066 deaths and over $11 billion in direct U.S. health care expenditures. Over the past decade, VHA has provided bariatric surgery to over 1000 severely obese veterans in 12 approved VHA Medical Centers in the hopes of improving their body weight, health, longevity, and potentially also reducing their health care expenditures. The proposed study builds on our prior work by addressing several novel research questions after bariatric surgery was integrated into the MOVE! program. First, our study will address the rate of resolution of diabetes, hypertension, and hyperlipidemia. Prior studies of this question have had many limitations, including a lack of a non-surgical control group, a lack of laboratory and blood pressure data to confirm resolution of comorbidities, and a focus on out-dated bariatric procedures. Second, it will follow patients over an entire decade of care (2000-2010) to establish the long-term durability of these health improvements, including the durability of weight loss, which has been poorly characterized in the literature. Third, our study will seek to identify patient-level characteristics that are associated with failures - failures to lose weight, failures to resolve comorbidities, and failures to achieve long- term weight maintenance - in an explicit attempt to identify important factors associated with less desirable health and economic outcomes. Using new clinical and laboratory data and expanding our prior datasets farther in time, the proposed study will build on our prior work in three primary aims: Aim 1: Compare weight change and resolution of diabetes, hypertension, and hyperlipidemia between veterans who had bariatric surgery and a matched cohort of severely obese veterans who did not have bariatric surgery in 2000-2010, and examine the durability of weight change and disease resolution among surgical cases. Aim 2: Compare long-term survival between veterans who had bariatric surgery and a matched cohort of severely obese veterans who did not have bariatric surgery in 2000-2010, and examine trends in major surgical complications among surgical cases. Aim 3: Compare long-term trends in VA health care utilization and VA expenditures between veterans who had bariatric surgery and a matched cohort of severely obese veterans who did not have bariatric surgery in 2000- 2010. The immediate objective of the proposed study is to expand our prior work by increasing our cohort size and observing them for a greater duration of time to allow examinations of ten-year survival, health care use, and expenditures and the long-term durability of changes in weight and resolution of comorbidities. The longer- term objective of the proposed study is to identify veterans who are ideal candidates for bariatric surgery and veterans who may not be well served by bariatric surgery because of their high risk for surgical complications and mortality or because of their modest response to surgery in terms of weight change and/or disease resolution. Finally, the proposed study is highly responsive to the HSR&D Priority Area of Health Care Access/Rural Health.